#include<bits/stdc++.h> using namespace std; int main(){ string x; cin>>x; if(x[0]>=48&&x[0]<=57){ cout<<"no"; return 0; } for(int i=0;i<=x.size()-1;i++){ if(((x[i]>=65&&x[i]<=90)||(x[i]>=97&&x[i]<=123)||x[i]=='_'||(x[i]>=48&&x[i]<=57))==0){ cout<<"no"; return 0; } } cout<<"yes"; return 0; }